At which point why would wouldn't a new company form to compete with them? They probably couldn't kill the market forever, and it would be very expensive to try this and fail.
That'd be the illegal part of being a monopoly. The antitrust laws work by restricting (penalizing) monopolies from abusing their market position/dominance.
Basically, it's not a problem if you happen to be the best in computers. But it's a big no-no to try to force resellers into exclusive contracts and so on. (If you continue to just buy up newcomers to the market that's not a problem, after all investors can just keep funding new competitors and you have to waste money.)
But of course this is a very difficult problem at the intersection of economics, politics, law and sociology.
Basically, it's not a problem if you happen to be the best in computers. But it's a big no-no to try to force resellers into exclusive contracts and so on. (If you continue to just buy up newcomers to the market that's not a problem, after all investors can just keep funding new competitors and you have to waste money.)
But of course this is a very difficult problem at the intersection of economics, politics, law and sociology.